I've been using my iPad as my primary computer almost exclusively the last year and it's great for content consumption but also pulls its weight in content production too. The major limitations for me with the iPad were back-ups, over the air OS updates, and lack of video conferencing. But those have now all been covered with iOS 5 and iPad 2's addition of a camera.
Every other limitation is of the maturity of software; both of the OSiOS needs a universal file system and I believe this is likely Apple's next priorityand of the software on the App Store. Image editing apps are not at the feature level of Photoshop but they're catching up, one update at a time.
And to answer the OP's question: yes, there are web development apps. Some are actually awesome and better than most desktop equivalents.
On a computer websites load in fractions of a second while the ipad still takes around ten seconds to load.
Woahhh. Ten seconds? My iPad never takes that long to load a page. In fact, Safari on my iPad is considerably faster than Safari on my Mac after a few tabs are opened.
Third is compatibility. The iPad has so many limitations as far as compatible software, accessory ports, and limited file management/file software support. So if you find something you like online, you can't download it, you can't view flash as well a certain kinds of java or direct x software, you cant get music on you device outside of iTunes, you cant have any type cd or DVD support, you're limited to what's in the app store for programs.
How are accessory ports a problem? Generally the things people wish to plug in are supported via a dock adaptor.
I've lived Flash-free for a year now, and anything I've been unable to view on my iPad has not been important enough to worry about. I'm not saying this experience will be the same for everyone, but it certainly will be for 99% of users.
You do have access to entertainment from other sources. There are many music apps and browsers that let you download files. I've even had musicians link me to a mediafire.com URL, where I go through the captcha process, download their song in a zip file, unzip the folder, then listen to the mp3 and transfer it to other apps. Granted, I am unaware if it's possible to put music into the native Music app in iOS 5, but a universal file system is surely coming and will make this possible. Lots of other options in the mean time.
Forth is what has been mentioned before, and that is creation. If you want to write a report, it's just much easier to do on a computer, and not just because of the keyboard. On a computer you can have a bunch of resource websites open, have your word proccessor (word, pages, ect.) and just go back and forth between them all so quickly and effortlessly. Sure you could write on the iPad, but it's a lot more trouble.
I think the switch app gesture makes this much simpler on iOS 5. Some form of split-screening would be nice in the future though, you're right.
I managed to write a resume on Pages for iPad. Done. I can email it, but I can't attach it to job search websites! 😡
As someone said, the iCab browser lets you upload files to websites. I've uploaded photos and files using iCab. Another option is to check if the job search website has its own app.